Gibson apparently planned to retire a couple of years ago but deferred the decision because of Peter Jennings's illness and problems with a planned two-anchor format. awyer could reasonably be considered ABC's biggest current news star, so it makes sense that she would get the big show. Changes take effect in January. Full report from ABC News after the jump, followed by a 2006 story I wrote about Gibson.

The ABC report:

Charles Gibson, who has served as anchor of "World News" since May of 2006, announced this morning that he will step down from the post at the end of this year and retire from full-time employment at ABC News.

"It has not been an easy decision to make," Gibson said in an e-mail to the "World News" staff. "This has been my professional home for almost 35 years. And I love this news department, and all who work in it, to the depths of my soul."

ABC News President David Westin said that he and Gibson have been talking about the decision for several weeks and that Gibson "has persuaded me that this is both what he wants and what is best for him."

"I respect his decision, just as I respect the enormous contribution he has made to ABC News through the years," Westin said.

Westin also announced Sawyer's move to "World News."

"Diane Sawyer is the right person to succeed Charlie and build on what he has accomplished," ABC News Westin said in a statement. "She has an outstanding and varied career in television journalism, beginning with her role as a State Department correspondent and continuing at 60 Minutes, Primetime Live, and most recently Good Morning America."

Westin noted that Gibson came to lead World News "after a difficult and turbulent time" after the death of anchor Peter Jennings and then injury of World News co-anchor Bow Woodruff by a roadside bomb that struck his vehicle near Taji, Iraq.

Charles Gibson Steps Down from 'World News'

Gibson, who previously co-hosted "Good Morning America along with Sawyer, had originally planned to step down in 2007.

"But with Peter's illness, Bob's injuries, and Elizabeth [Vargas's] pregnancy, the job at World News came open in May of 2006," Gibson said the e-mail to ABC staff. He was asked to step in as anchor. "It was an honor to do so."

Sawyer has interviewed every president since President George H. W. Bush, including President Obama, and has handled an array of breaking news special events, including on Sept. 11 and, most recently, the 2008 presidential election.

Here's the story I wrote about Gibson in 2006:

When ABC anchor Charles Gibson said 2008 is going to have "a great election," or summed up his work online as "sorta neat," I started to think, yes, I could watch this guy deliver the nightly news. In fact, Gibson is delivering so much news that ABC on Wednesday dropped the "tonight" from World News Tonight to emphasize its round-the-clock news presence on TV, radio and the Internet. It also finally added With Charles Gibson to the title, a phrase that has been a long time coming. Gibson has been at ABC for more than 30 years. He was offered the main anchoring job at ABC after the death of Peter Jennings, but only as a temporary thing while ABC News President David Westin figured out the next step in news formats. "I said if people know when you're going to get out of the chair, before you even get into the chair, you never really have the job," Gibson said. "So we agreed to disagree." ABC instead went with the dual-anchor system of Bob Woodruff and Elizabeth Vargas, only that system was derailed when Woodruff was seriously injured in Iraq. (Woodruff is working his way back, and spent the last couple of days in the ABC newsroom in New York City.) When Vargas became pregnant, ABC decided to go back to Gibson. Recently schooled in daytime television as co-host of Good Morning America, Gibson brings freshness and enthusiasm to his role as the main face of ABC News even if that role means going into harm's way. He and World News executive producer Jon Banner talked to reporters via satellite from Cyprus. Nor does his pleasure mean that he is lightweight. He is on occasion unapologetically detail-minded, comparing 2008 to the 1952 campaigns, or ending a dissertation on gerrymandering with the declaration that "I don't think anybody (at the press conference) cares about this, but I do." And he regretted being back in the Middle East. "I've been here so many times," he said, "and usually when you come, it's because there has been something tragic. . . . This is certainly a perilous time. . . . I think it's going to be a number of days before we see a resolution to what's going on. And of course the great peril is that this kind of fighting could widen before it's actually settled." Gibson's presence in Cyprus invited questions about traveling anchors -- questions that are not new, by the way. Gibson noted that he had forgotten his passport Wednesday morning, and that he suspected the late Peter Jennings "never did that." As for when an anchor should travel to hot spots, Gibson said, "I don't have an answer to the question. It's sort of the situation where we'll know it when we see it. . . . Last week, as the situation was developing here, we just had a sense that this was going to be the place we ought to be." But he feels that an anchor dropping into the middle of a trouble zone is not necessarily the newscaster with all the answers. "It's better if you've got people in place," he said. "We've got a terrific Mideast bureau, and . . . the people that we have in the region know the region best. And so if I come in or Katie (Couric) comes in or Brian (Williams) comes in . . . I think probably it calls more attention to the story, but I'm very mindful of the fact that the people who regularly cover the beat know it best." At the same time, Gibson said going to a region can be a "tremendous learning experience," especially when it comes to meeting the players in a rapidly changing scene. Reporters also asked Gibson about another group of players: Couric, who begins anchoring CBS's news in the fall, NBC's Brian Williams and Gibson himself. Gibson says he has little interest in some of the details, that he doesn't understand the nuances of TV ratings, and he's not looking at the "Brian vs. Katie vs. Charlie" aspects of the situation. He knows Couric socially, and he and Williams "have had a couple of meals together, and I just have an enormous amount of respect for him. I think he's a terrific broadcaster." But in terms of organization versus organization, he said, "Let's get it on." "These are three great news organizations," he said. "I happen to think ours is the best."